A facile synthesis of ZnO nanotubes and their hydrogen sensing properties

A method is developed to easily synthesize hydrogen sensors based on zinc oxide nanotubes (ZNTs) at low temperatures. ZnO nanorods (ZNRs) are first synthesized using the aqueous chemical process at 90 °C for 3 h, and then cools and maintains at 50 °C for 6, 12 and 18 h in three separate batches. ZNRs are then transformed to ZNTs after the low temperature selective self-etching process. SEM, XRD and PL spectroscopy are respectively used to analyze surface morphology, crystallinity and optical properties. The pristine ZNR sensors and ZNT sensors are then measured for hydrogen response in concentrations from 5 to 500 ppm at room temperature. The ZNTs can provide a larger surface area (i.e., through assuming a hollow nanostructure) than the pristine ZNRs for adsorbing additional gas ions, along with more oxygen vacancies to effectively sense gas ions as t increased from 6 to 18 h. It is found that the hydrogen response of all ZNT hydrogen sensors is about 2 times higher than that of the pristine ZNR sensor (13.1%, at 500 ppm) at room temperature. The ZNT sensor for t = 18 h exhibits the highest oxygen vacancies and provide the best response for hydrogen sensing (29.6%, at 500 ppm).